Hydrodynamic contaminant isolation for light modulating fluid



Jan. 13, 1970 H. E. TowLeoN 3,489,940

HYDRODYNAMIC CONTAMINANT ISOLATION FOR LIGHT MODULATING FLUID FiledMarch28, 1969 2 Sheets-Sheet 1 HOWARD E. TOWLSON,

BY HIS ATTOR EY.

Jan. 13, 1970 H. E. TOWLSON I 3,489,940

HYDRODYNAMIC CONTAMINANT ISOLATION FOR LIGHT MODULATING FLUID FiledMarch 28, 1969 2 Sheets-Sheet a INVENTOR HOWARD E. TOWLSON,

fl BY HIS ATTORNEY.

United States Patent 3,489,940 HYDRODYNAMIC CONTAMINANT ISOLATION FORLIGHT MODULATING FLUID Howard E. Towlson, Baldwinsville, N.Y., assignorto General Electric Company, a corporation of New York Filed Mar. 28,1969, Ser. No. 811,430 Int. Cl. Hillj 29/12 US. Cl. 31391 9 ClaimsABSTRACT OF THE DISCLOSURE Isolation from contaminants of a lightmodulating fluid layer on the rotatable disk of a light valve isachieved by use of a baflle plate spaced in close proximity to, andparallel to, the disk. Fresh filtered fluid dispensed from a channel ofpartially closed configuration on the side of the plate facing the diskmaintains a fluid buffer region around the area of the disk whereon thefluid layer is to be deformed by an electron beam. The buffer region,contained between the plate and the disk, prevents contaminated,particulate-carrying sump fluid from reaching the disk surface.

Introduction This invention relates to light valves for opticalprojection of images generated electronically on a fluid layer, and moreparticularly to a system for isolating from contaminated fluid the fluidlayer upon which diffraction gratings corresponding to the images to beprojected are formed.

One form of light valve suitable for optical projection ofelectronically generated images onto a remote display surface comprisesan evacuated envelope containing an electron gun in alignment with atransparent disk. The disk is rotated through a reservoir of lightmodulating fluid to deposit a continuously replenished layer of fluid onthe disk surface. An electron beam, generated by the electron gun, isdirected through electrostatic beam defleeting and focusing means and isscanned across a portion of the light modulating fluid layer so as toselectively deform the layer. The fluid deformations thus formedconstitute diffraction gratings which, in conjunction with a Schlierenoptical system, selectively control passage of light from a light sourcethrough the disk and through an output window in the light valveenvelope in order to create visible images at a remote display surfaceon which the light impinges.

Light valves of the type described have hitherto operated satisfactorilyonly for limited periods of time. Although the light modulating fluid isfree from particulate contamination at the outset of light valveoperation, a buildup of contamination occurs as operation of the lightvalve progresses. This contamination is due mainly to wear of movingparts within the light valve, as well as presence of impurities. Inaddition, some particles are formed as a result of massive damage tofluid molecules caused by heavy electron or ion bombardment. Eventuallythis contamination reaches a level which results in appearance ofobjectionable spots in the displayed image, since the particles presentin the fluid tend to accumulate on the disk.

To overcome the problem of contamination, fluid filtering systems havebeen added to light valves. These systems permit flushing of the diskswith fresh filtered fluid, thereby greatly extending the usefullifetimes of the disks. However, the flow rate of a flushing system isso high as to require a fluid reservoir, pump, and filter, all of largefluid-handling capacity. Consequently, at least a portion of theflushing system must be kept outside the envelope 3,489,940 PatentedJan. 13, 1970 in order to maintain the volume of the envelope withinpractical size; that is, within a size which does not requireextraordinarily large envelope wall thicknesses and which, duringfabrication of the light valve, permits pumpdown or evacuation of theenvelope within a reasonable time.

The present invention concerns a light valve in which a portion of thedisk rotates through a sump containing the light modulating fluid.Apparatus is provided for hydrodynamically isolating the lightmodulating fluid layer on the disk from the contaminated,particulate-carrying sump fluid in order to prevent the sump fluid frommixing with the fluid layer on the disk surface. By situating a baflleplate in close parallel proximity to the disk and dispensing fluid froma channel of predetermined confiuration on the side of the baffle platefacing the disk, a low fluid flow rate is suflicient to maintain freshfiltered fluid within the entire region between the baflie plate and thedisk. Only fresh filtered fiuid is thus picked up by the disk eventhough the region between the baflle plate and the disk is situatedwithin the sump.

Accordingly, one object of the invention is to provide a system fordispensing light modulating fluid in a light valve so as to require onlya low volume filtering system for the fluid.

Another object is to provide apparatus for isolating the lightmodulating fluid layer on the surface of a rotating disk in a lightvalve from contaminated light modulating fluid.

Another object is to provide a light valve wherein the entire volume oflight modulating fluid is maintained wholly within the light valveenvelope.

Briefly, in accordance with a preferred embodiment of the invention, alight valve containing a rotatable disk, 9. layer of light modulatingfluid coated on one surface of the disk, and a sump containing lightmodulating fluid are provided, with a portion of the disk beingsubmerged in the sump. Apparatus for hydrodynamically isolating thelight modulating fluid layer on the one surface of the disk from thecontaminated fluid so as to prevent contaminated fluid from coating theone surface comprises a baflle plate spaced in close proximity to theone surface of the disk. The baflle plate is at least partiallysubmerged in the sump and situated substantially parallel to the onesurface of the disk. A fluid conveying means being open along its lengthis disposed in predetermined configuration on the side of the baffleplate facing the disk. Means coupled to the fluid conveying means areprovided for furnishing fresh filtered fluid thereto.

Brief description of the drawings The features of the invention believedto be novel are set forth with particularity in the app nded claims. Theinvention itself, however, both as to organization and method ofoperation, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconjunction with the accompanying drawings in which:

FIGURE 1 is a partially cutaway side View of a portion of a light valveshowing the hydrodynamic contaminant isolation means of the instantinvention; and

FIGURE 2 is a sectional view taken along line 22 in FIGURE 1.

Description of typical embodiments FIGURE 1 illustrates a light valvecontaining the hydrodynamic contaminant isolation means of the instantinvention. The light valve comprises an envelope 10, typically comprisedof glass, containing a light output window portion 11 and a sump region12 holding a reservoir of light modulating fluid 13. The interior ofenvelope 10 is evacuated to a low gas pressure.

The light modulating fluid is typically of the polybenzyltoluene typehaving a fluid viscosity of 1,000 centistokes at 60 C., with a vaporpressure in the range of 10 torr. The fluid contained in sump region 12is that which has drained off an optically transparent disk 14 which iscontinuously rotated on bearings 15 about a shaft 16, typically at aspeed in the order of 3 revolutions per hour. A spring is maintained incompression by having its cap 21 aflixed to a rigid support member 22which, in turn, is affixed to envelope 10 of the light valve by anysuitable means (not shown). The opposite end of spring 20 bears againstthe body of shaft 16. Consequent- 1y, a shoulder 23 on shaft 16 urgesbearings 15 to force disk 14 against a plurality of protuberances 17,which may advantageously be formed of fritted glass droplets. Theseprotuberances are aifixed to output window 11.

Disk 14 is spaced apart from light output window 11 by a distance ofabout 3 mils so as to permit fluid 18 from sump 12 to rise by capillaryaction and fill the region between the disk and the output window. The 3mil spacing is maintained by protuberances 17, as described in greaterdetail in H. E. Towlson Patent 3,385,991, issued May 28, 1968 andassigned to the instant assignee. As pointed out in the aforementionedTowlson patent, adverse effects produced by either a non-uniform fluid cating on the output surface of the rotatable disk, or by fluidcondensate or droplets on the output window, are thereby eliminated.

A thin film 24, which comprises a transparent conduc tive coating suchas indium oxide, is carried on rotating disk 14. Coating 24 may bemaintained at any desired potential since a conductive path is formedthrough bearing 15, shaft 16, spring 211, cap 21 and member 22,permitting a continuous electrical connection to coating 24 through astationary connection (not shown) which may be made to member 22. Anaperture 19 in member 22 permits passage of an electron beam 25,originating at an electron gun 26, to be directed toward conductivecoating 24 on disk 14. Disk 14 itself is non-conductive, and preferablyis comprised of glass.

A think film of light modulating fluid 27 is coated on thin film 24 andthus is situated in the direct path of electrons in electron beam 25.Beam 25 is focused and deflected by electron optical means (not shown)within the light valve and hence is swept, in raster fashion, over thesurface of light modulating fluid layer 27. The pattern of charges onlayer 27 produced by electron beam 25 causes corresponding deformationsin the thickness of layer 27, resulting in formation of diffractiongratings 30. These gratings correspond to the image to be projected ontoa remote display surface. Light from a light source (not shown)positioned behind electron gun 26 impinges upon a lenticular lens system28 formed on the rear wall of envelope 10 and is directed by thelenticular lens system through aperture 19 onto diffraction gratings 30.

By modulation of electron beam 25 through application of suitablepotentials to the electrostatic focus and deflection means, diffractiongratings 30 in fluid layer 27 are selectively controlled. Consequently,light passing through transparent rotatable disk 14 and output Window 11is selectively controlled and, in conjunction with eX- ternally locatedlenses of a Schlieren optical system (not shown) is projected on aremote display surface (not shown) to form an image representative ofthe intelligence modulating the electron beam.

A baflle plate 40, situated within sump 12, is spaced in close proximityto, and parallel to, disk 14. The spacing and orientation of baflleplate with respect to disk 14 are maintained by spacer bars 41. Byemploying a metallic baffle plate, bars 41 may be Welded to the battleplate and mated with cavities 42 in output window 11. The baflie plateis then rigidly held in place by two spring clips 43.

The manner by which spring clips 43 hold baffle plate 40 to outputwindow 11 is further illustrated in FIGURE Ill 2, which is a sectionalview taken along line 22 of FIGURE 1. In FIGURE 2 the Width of baflleplate 40 can be seen to be larger than that of disk 14, while outputwindow 11 can be seen to have protruding regions 47 which position bars41 and clips 43 at locations to avoid interference with rotation of disk14. Baflle plate 40 may alternatively be constructed of glass, in whichcase spacer bars 41 are likewise constructed of glass and joined byfritling to output window 11. Construction of this alternative typerenders spring clips 43 unnecessary. The separation maintained betweenbaflle plate 40 and disk 14, whether the battle plate he constructed ofmetal or glass, is typically in the order of 10-15 mils.

Fluid conveying means 44 is disposed in predetermined configuration onthe side of baffle plate 41 facing disk 14. This configuration is suchas to permit flow of fresh filtered fluid outward in all directionsparallel to the plane of disk 14, so as to maintain the entire regionbetween disk 14 and output Window is 11 filled with fresh filtered fluidonly. By continuing to supply fresh filtered fluid from a pump andfilter 45, shown in FIGURE 1, through a closed tube 4'6 to fluidconveying means 44, fluid pressure in the region between baflle plate 40and disk 14 is maintained sufliciently high to prevent contaminatedfluid from sump 12 from entering this region. Accordingly, as disk 14rotates. transparent coating 24 is continually covered with freshfiltered fluid only, since the surface of coating 24 does not contactany of the contaminated fluid in sump l2.

Fluid conveying means 44 preferably comprises an open channel recessedwithin the baflie plate so as to avoid any projecting surfaces on baflleplate 40 which might impede flow of fresh filtered fluid in any of thedirections parallel to the plane of disk 14. This also helps to avoidturbulence in the outward flow of fluid from conveying means 44. Suchturbulence could have the undesirable effect of mixing contaminatedfluid from sump 12 with the fresh filtered fluid emerging from fluidconveying means 44, thereby adding contaminants to fluid layer 27.

The configuration of fluid conveying means 44 may conveniently bepartially closed, such as arcuate, in form and situated within a volumeadjacent to the area of disk 14, as shown in FIGURE 2. Accordingly,substantially the entire portion of the surface area of transparentconductive coating 24 submerged in fluid 13 is coated only with freshfiltered fluid.

A raster area 48 on oil film 27, which is the region upon which electronbeam 25 may impinge to form diffraction gratings 30, is illustrated inits relative position on disk 14 in FIGURE 2. Although raster area 48 isshown as a discrete area, and is fixed with respect to output window 11,those skilled in the art will recognize that the raster area on disk 14constitutes a circular band, due to the continuous rotation of the disk.Accordingly, with respect to disk 14, area 48 is merely an instantaneousregion which conveniently aids in describing operation. It can be seenthat with disk 14 rotating, as in the direction indicated by the arrow,instantaneous raster area 48 passes within close range of groove 44 fora period of roughly one-third of a revolution of disk 14. During thisperiod, the instantaneous raster area is maintained in hydrodynamicisolation from contaminants contained in the sump fluid. During theremaining two-thirds of each revolution, the instaneous raster area isoutside the sump fluid.

By spacing baffle plate 40 at a distance of only 10-15 mils from disk24, flow of fluid outward from fluid conveying means 44 provides twofoldbenefits. First, only a very small flow rate is required to maintain theentire submerged surface of transparent conductive coating 24 coveredwith only fresh filtered fluid. This is because the volume of freshfiltered fluid required to completely fill the region between baflieplate 40 and disk 14 is quite small. This low volume and low flow ratenecessitate but a small fluid pump and small filter capacity, enablingthe pump and filter to be situated within envelope 10 of the lightvalve. The pump may be driven by a magnetic coupling (not shown) throughglass envelope 10, so that no external mechanical connection need bemade to the pump and filter. This reduces the requirements forglassto-metal seals, thereby simplifying construction of the lightvalve. The action of the magnetic coupling on the pump of pump andfilter means 45, moreover is such as to attract the pump tightly againstenvelope at the region where the magnetic coupling is being made, sothat no additional means are required to maintain pump and filter means45 in proper position. The flow of fluid to and from pump and filtermeans 45 is indicated by the arrows in FIGURE 1.

The second benefit of closely spacing baffle plate 40 from disk 14 isthat a laminar flow of fluid outward from fluid conveying means 44 isachieved. This flow is uniform over the entire length of fluid conveyingmeans 44. The advantage of a uniform laminar flow is that turbulence isavoided and hence no mixing of the fresh filtered fluid with thecontaminated fluid from sump 12 takes place within the region enclosedbetween disk 14 and baffle plate 40. This insures that only freshfiltered fluid can reach the surface of transparent conductive coating24, so that spurious spots in the optically displayed image due toforeign particles in the diffraction gratings formed on oil film 27 areheld to a minimum indefinitely.

The fluid flowing at the low rate, which is in the order of 3 cubiccentimeters per minute, is distributed by making groove 44 in the orderof 100 mils wide, although the groove may be made as wide as 4 inchwithout detriment to the laminar flow therefrom. The cross-sectionalconfiguration of groove 44 may conveniently be rectangular and, for agroove of about 50 mils in depth, a metallic baflie plate ofapproximately inch thickness may be utilized.

The foregoing describes a low volume filtering system for the lightmodulating fluid of a light valve. The filtering system is containedentirely within the light valve, and is capable of withstanding a 450 C.bake in air, followed by a 400 C. bake in vacuum, both of which aretypically employed in fabrication of the light valve in which theinvention is utilized. The entire volume of light modulating fluid ismaintained wholly within the light valve envelope. Apparatus is providedfor isolating from contaminated light modulating fluid the lightmodulating fluid layer on the conductively-coated surface of therotating disk of a light valve.

While only certain preferred features of the invention have been shownby way of illustration, many modifications and changes will occur tothose skilled in the art. It is, therefore, to be understood that theappended claims are intended to cover all such modifications and changesas fall within the true spirit of the invention.

Iclaim:

*1. In a light valve containing a rotatable disk, a layer of lightmodulating fluid coated on one surface of said disk, and a sumpcontaining contaminated light modulating fluid, a portion of said diskbeing submerged in said sump, apparatus for hydrodynamically isolatingthe light modulating fluid layer on said one surface from saidcontaminated fluid so as to prevent contaminated fluid from coating saidone surface, said apparatus comprising:

6 means immersed in said sump and situated in close proximity to saidone surface of said disk so as to define a predetermined volume of fluidadjacent said one surface of said one surface of said disk; meanscommunicating with said volume and furnishing fresh filtered fluidthereto at a flow rate sufliciently high to prevent any of saidcontaminated fluid from entering said volume. 2. The apparatus of claim1 wherein said means communicating with said volume includes an openchannel situated within said sump and producing a laminar flow of fluidfrom the entire open portion of said channel.

3. In a light valve containing a rotatable disk, a layer of lightmodulating fluid coated on one surface of said disk, and a sumpcontaining contaminated light modulating fluid, a portion of said diskbeing submerged in said sump, apparatus for hydrodynamically isolatingthe light modulating fluid layer on said one surface from saidcontaminated fluid so as to prevent contaminated fluid from coating saidone surface, said apparatus comprising: a bafiie plate spaced in closeproximity to said one surface of said disk, said baflle plate being atleast partially submerged in said sump and situated substantiallyparallel to said one surface of said disk;

fluid conveying means disposed in predetermined configuration on theside of said b-aflie plate facing said disk, said fluid conveying meansbeing open along its length; and

means coupled to said fluid conveying means for furnishing freshfiltered fluid thereto.

4. The apparatus of claim 3 wherein said fluid conveying means comprisesan open channel recessed within said baflle plate.

5. The apparatus of claim 3 wherein said means fumishing fresh filteredfluid to said conveying means comprises a fluid circuit communicatingwith said sump for removing contaminated fluid from said sump, saidfluid circuit including fluid filtering means and fluid pumping means soas to filter fluid removed from said sump and furnish the filtered fluidto said conveying means.

6. The apparatus of claim 5 wherein said fluid conveying means comprisesan open channel recessed within said baflle plate.

7. The apparatus of claim 5 wherein said fluid circuit is whollycontained within said light valve.

8. The apparatus of claim 6 wherein said fluid circuit is whollycontained within said light valve.

9. The apparatus of claim 6 wherein the predetermined configuration ofsaid open channel is generally arcuate.

References Cited UNITED STATES PATENTS 2,776,339 1/1957 Arni 178-7.53,385,991 5/1968 Towlson 313-91 JAMES W. LAWRENCE, Primary Examiner V.LAFRANCHI, Assistant Examiner U.S. Cl. X.R.

